The organisms that cause nosocomial infections may originate from other patients, the hospital environment, medical personnel, or from the patient's own normal flora. Because of the widespread use of antimicrobial drugs in hospitals, many organisms that cause nosocomial infections are resistant to these medications.
Because of the very nature of hospitals, infectious agents are always present. Patients are often hospitalized because they have a severe infectious disease. The pathogens that these patients harbor can be discharged into the environment via skin cells, respiratory droplets, and other body secretions and excretions. Scrupulous cleaning and the use of disinfectants minimize the spread of these pathogens.
Some Gram-negative rods, particularly the common opportunistic pathogen Pseudomonas aeruginosa, can thrive in certain hospital environments such as sinks, respirators, and toilets. Not only is P. aeruginosa resistant to the effects of many disinfectants and antimicrobial drugs, it requires few nutrients, enabling it to multiply in environments containing little other than water. Many nosocomial infections have been traced to soaps, disinfectants, and other aqueous solutions that have become contaminated with the organism.
Outbreaks of nosocomial infections are sometimes traced to infected health care personnel. Clearly, those who report to work with even a mild case of influenza can expose patients to an infectious agent that has serious or fatal consequences to those with impaired health. A more troublesome source of infection is a health care worker who is a carrier of a pathogen such as Staphylococcus aureus or Streptococcus pyogenes. These personnel often do not recognize they pose a risk to patients until they have been implicated in an outbreak. Carriers who are members of a surgical team pose a particular threat to patients, because inoculation of a pathogen directly into a surgical site can result in a systemic infection.
Patient's Own Normal Flora
Many hospital-acquired infections originate from the patient's own flora. Nearly any invasive procedure can transmit microorganisms that are part of the normal flora to otherwise sterile body sites. When intravenous fluids are administered, for example, Staphylococcus epidermidis, a common member of the normal skin flora, can potentially gain access to the bloodstream. While the immune system can usually readily eliminate these normally benign organisms, the underlying illness of many hospitalized patients compromises their immunity and they can develop a bloodstream infection. Patients who undergo intestinal surgery are prone to surgical site infection by their normal bowel flora. Similarly, patients who are on cer-
tain medications or have impaired cough reflexes can inadvertently inhale their normal oral flora, resulting in hospital-acquired pneumonia.
Severely immunocompromised patients, such as people who have undergone cancer chemotherapy or are on immuno-suppressive drugs, are prone to activation of latent infections that their immune system was previously able to control. For example, latent infections of Toxoplasma gondii, a protozoan parasite commonly acquired during childhood, can become activated and cause a life-threatening disease. ■ latent infection, p. 463
Diagnostic and therapeutic procedures during hospitalization can potentially transmit infectious agents to patients. This is particularly true in intensive care units (ICUs), where patients generally have indwelling catheters used to deliver intravenous fluids or monitor the patient's condition (figure 20.12).
Nosocomial infections most often result from medical devices that breach the first-line barriers of the normal host defense. For example, catheterization of the urinary tract can readily introduce microorganisms into the normally sterile bladder. Because urine is an excellent growth medium, the urinary tract often becomes infected. Urinary tract infections are the most common type of nosocomial infection (see figure 20.11).
Just as urinary catheters can introduce bacteria into the bladder, intravenous (IV) catheters can introduce micro organisms into the bloodstream. This can happen when normal skin flora colonize the tip of an indwelling catheter or when environmental organisms contaminate IV fluids or the lines that deliver them. Even normally benign skin flora can cause life-threatening bacteremia when they gain access to the bloodstream.
Mechanical respirators that assist a patient's breathing by pumping air directly into the trachea can potentially deliver
microorganisms to the lungs. This is particularly a problem if a nutritionally versatile organism such as Pseudomonas can gain access to water droplets in the machine, allowing it to multiply.
Inadequately sterilized instruments that are used in invasive procedures such as surgery or biopsy can also transmit infectious agents. Endoscopes and other heat-sensitive instruments are often treated with chemical sterilants to render them microbe-free. Improper use of these chemicals, however, can result in the survival of some organisms. ■ sterilants, p. 117
Health care personnel must be extremely vigilant to avoid transmitting infectious disease agents, particularly from patient to patient. What Ignaz Semmelweis found to be true in the 1800s is equally true today—handwashing between contact with individual patients helps prevent the spread of disease (see A Glimpse of History). Unfortunately, this relatively simple procedure is too often overlooked.
Health care personnel should routinely wash their hands after touching one patient before going on to the next. A more thorough hand scrubbing, requiring 10 minutes and using a strong disinfectant, should be performed by nurses, physicians, and other personnel before participating in an operation, or when working in a nursery, or intensive care or isolation unit. Gloves are also worn whenever there is contact with blood, mucous membranes, broken skin, or body fluids.
Most hospitals are designed to minimize the airborne spread of microorganisms. For example, the airflow is usually regulated so that it is supplied to the operating room under slight pressure, thereby preventing contaminated air in the corridors from flowing into the room. Floors are washed with a damp mop or floor washer rather than swept in order to avoid resuspending microbes into the air.
To exclude airborne microorganisms and viruses from rooms in which exquisitely susceptible patients reside, such as those who have recently undergone a bone marrow transplant, high-efficiency particulate filters (HEPA) are employed. These filter out most airborne particles, including microorganisms. ■ HEPA filters, p. 122
The most important steps in preventing nosocomial infections are to first recognize their occurrence and then establish policies to prevent their development. To accomplish this, nearly every hospital has an Infection Control Committee, composed of representatives of the various professionals in the hospital, such as nurses, physicians, dietitians, housekeeping staff, and microbiology laboratory personnel. On this committee, and sometimes chairing it, is often a hospital epidemiologist, a professional specially trained in hospital infection control. Hospitals may also employ an infection control practitioner (ICP), whose role is to perform active surveillance of the types and numbers of infections that arise in the hospital. The Infection Control
PERSPECTIVE 20.1 Standard Precautions—Protecting Patients and Health Care Personnel
One of the biggest challenges for a hospital has always been the prevention of spread of disease within that confined setting. A century ago, patients with infectious diseases were segregated in separate hospitals; those with similar diseases were sometimes housed in clusters on the same floor. In 1910, a cubicle system of isolation was introduced in which patients were placed in multiple-bed wards. Aseptic nursing procedures were aimed at preventing the transmission of infectious agents to other patients and personnel.These scrupulous measures were so successful that general hospitals were able to incorporate infectious disease patients, ultimately resulting in the closure of many infectious disease hospitals beginning in the 1950s.To assist general hospitals with isolation procedures, in 1970 the CDC began publishing a manual that recommended a category system of seven isolation procedures for patients based on their diagnosis.These procedures included Strict Isolation, Respiratory Precautions, Protective Isolation, Enteric Precautions, Wound and Skin Precautions, Discharge Precautions, and Blood Precautions. Over the years, some of these categories were changed or deleted.
In the early 1980s it became increasingly apparent that health care workers were acquiring hepatitis B and, later, HIV from contact with the blood or other body fluids of patients, including those who were not suspected of having blood-borne disease. Existing guidelines were primarily aimed at preventing patient-to-patient transmission of disease, rather than patient-to-personnel. In response, the CDC recommended an additional set of guidelines, the Universal (Blood and Body Fluid) Precautions, to be followed when working with any patient, regardless of the diagnosis.These defined the situations in which gloves, gowns, masks, and eye protection were required to prevent contact with blood. Many hospitals then broadened this concept, requiring the use of gloves to isolate all moist and potentially infectious body substances.This approach, Body Substance Isolation, made the traditional diagnosis-dependent isolation procedures largely unnecessary.
The advent of Universal Precautions and Body Substance Isolation, in addition to the previous diagnosis-dependent isolation procedures, resulted in a such a mix of recommendations that it generated a great deal of confusion. No existing single set of guidelines was sufficient, and it was not clear which one should be used when. In response, the CDC and the Hospital Infection Control Program Advisory Committee established a new set of guidelines in 1996 that incorporates the strength of each of the alternatives.These new guidelines have two tiers of isolation procedures.The fundamental measures are the Standard Precautions, designed for the care of all patients in all hospitals.The Transmission-Based Precautions are supplementary measures to be used in addition to the Standard Precautions if a patient is, or might be, infected with highly transmissible or epidemiologically important pathogen.These are separated into three sets—Airborne Precautions, Droplet Precautions, and Contact Precautions—which are used singly or in combination as appropriate.
The Standard Precautions can be summarized as:
Handwashing. Wash hands with soap and water after touching blood, body fluids, secretions, excretions, and contaminated items, whether or not gloves are worn.
Gloves. Clean disposable gloves are worn whenever there is possible contact with blood, body fluids, secretions, excretions, mucous membranes, skin wounds, and contaminated items. Change gloves between procedures on the same patient after contact with material that may contain high concentrations of microbes. Remove gloves immediately after use and wash hands thoroughly. Gloves should always be removed in a reverse manner so as not to touch the contaminated surface.
Mask, eye protection, face shield, gown. When doing a procedure that is likely to generate splashes or sprays of blood, body fluids, secretions, and excretions, wear a mask and eye protection or a face shield to protect the mucous membranes of the eyes, nose, and mouth. Wear a clean gown. Remove the soiled gown as soon as possible and wash hands.
Patient-care equipment. Handle used patient-care equipment soiled with blood, body fluids, secretions, and excretions in a manner that prevents skin and mucous membrane exposure, and contamination and transfer to other patients and environments. Reusable equipment must be cleaned and processed appropriately. Single-use items must be disposed of properly.
Environmental control. Use adequate procedures for the routine care, cleaning, and disinfection of environmental surfaces, bed rails, and other frequently touched surfaces.
Linen. Soiled, reusable items are placed in protective bags to prevent leaking and contamination.
Occupational health and blood-borne pathogens. All needles and sharp objects are discarded in a rigid, puncture-proof container without touching them or replacing needle caps.
Patient placement. Private rooms are used for any patient who contaminates the environment or might soil other people and their surroundings.
From: http://www.cdc.gov/ncidod/hip/ISOLAT/Isolat.htm The Public Health Services, U.S. Department of Health and Human Services, Centers for Disease Control and Prevention. Garner, J. Hospital Infection Control Practices and Advisory Committee. Guidelines for Isolation Precautions in Hospitals. Infection Control and Hospital Epidemiology 1996; 17: 53-80, and American Journal of Infection Control 1996; 24: 24-52.
Committee, in conjunction with the ICP, drafts and implements preventative policies following the guidelines suggested by the Standard Precautions and the Transmission-Based Precautions (see Perspective 20.1).
The CDC also takes an active role in preventing nosocomial infections and in the early 1990s established the Hospital Infection Control Program Advisory Committee (HICPAC). The role of this national committee is to provide advice to hospitals and recommend guidelines for surveillance, prevention, and control of nosocomial infections.
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